Furnace



March 31, 1931.v RC. KELLEY 1,799,102

FURNACE Filed Aug. 15, 1929 Inventor: Flogd C Kelley,

His Attorney'- Patented Mar. 31, 19 31 UNITED STATES PATENT OFFICE FLOYD G. KELLEY, F SCHENECTAIDY, NEW YORK, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A CORPORATION OF YORK FURNACE Application filed August 13, 1929. Serial No. 385,519.

My invention relates to furnaces, more particularly to high temperature furnaces,

and has for its object the provision of a simple and rug ed furnace which is particw larly adapted for the carrying out of high able gas which prevents oxidation, the maxi mum temperature may be limited by the melting point of the resistor element or by the heat refractory characteristics of other parts of the furnace.

In accordance with my invention I provide means associated with the furnace for continuing the heating operation so as to increase the temperature of the charge itself, as desired, without, however, subjecting the furnace itself to this increased temperature.

In one form of my invention I induce heat in the charge itself-by high frequency induction.

For a more complete understanding of my invention reference should be had to the accompanying drawing, the single figure of which is a'diagrammatic view, partly in section, of an electric furnace embodying my invention.

Referring to the drawing, in carrying out my invention in one form I provide an induction winding or coil 10 which surrounds the 4 furnace 11 of a suitable form. This coil constitutes an auxiliary source of heat for the charge in the furnace by virtue of its magnetic field which induces heating currents in the charge itself. It will be understood that the number of turns in the coil 10 and other characteristics of the coil will be suitably selected to correspond with the frequency of the alternating currents supplied thereto from a suitable source 10*. Preferably high frequencies in the neighborhood of 500 cycles or more will be used. The main controlling requirement is that the frequency be high enough so that no magnetic core need be provided for the coil 10. As shown, the coil is wound on a cylindrical support 12 made of a suitable heat refractory electrically insulated material such as asbestos or alumdum. This support is slipped over the furnace 11, which also is shown as cylindrical in shape, and fits loosely on the furnace 11.

While obviously my invention may be car- .ried out with a furnace 11 of any suitable construction and heated in any suitable manner, I have shown the furnace 11 as an electric furnace comprising an inner tubular member 13 made of a suitable heat refractory electrical insulating material such as alumdum, i. e., aluminum oxide, the interior of this tube constituting the heating chamber 14:. On the exterior of the tube 13 is wound a heating resistor wire 15 which is made of a suitable material, such as a nickel chromium alloy or preferably molybdenum. This tube 13 and the resistor are surrounded by an outer alumdum casing 16 of considerably larger diameter, the space between the two being filled with a'suitable granular heat refractory insulating material, such as aluminum oxide. At the ends the space between the tubes 13 and 16 is closed by discs 17 and 18 made of a suitable heat refractory material such as asbestos cement. In order to protect the heating resistor 15 from oxidation at high temperatures, a suitable gas,

such as hydrogen, is passedinto the casing 16 by means of a conduit 19, an outlet conduit 20 being. also provided. The gas seeps through the granular insulating material driving out the air and thus surrounding the resistor with a non-oxidizing atmosphere,

substantially as described and claimed in the Coolidge Patent 1,004,557.

In the operation of the furnace the charge 21 to be heated is placed in the heating chamher and at first heated by means of the resistor 15 which is connected to a suitable source of electrical supply having a normal low frequenc such as 60 cycles. It will be understood t at the furnace is provided at each end with suitable closing means, shown as removable plugs 22 and 23. Furthermore, an atmosphere of hydrogen or other inert gas is preferably maintained in the heating chamber by means of the inlet and outlet conduits 24 and 25. The charge, as shown, consists of a terminal 26 which is to be brazed at the point 27 t0 the tungsten filament 28 of a vacuum tube. As shown, the terminal and filament are inserted into the heating chamber through an aperture 29 in the plug 23. v

The heating operation continues with the resistor 15 as the source of heat until the charge temperature is approximately the same as the temperature of the furnace after which, of course, no further increase in temperature takes place. In this particular furnace, operating with an atmosphere of hydrogen, the temperature limiting characteristic is inherent in the alumdum tube 13 which tends to become soft at about 1700 degrees C. Consequently the maximum temperature to which it may safely be subjected is approximately 1600 degrees C. .which therefore is the maximum temperature at which the furnace can be operated. If desired, suitable control means may be provided for limiting the temperature automatically to a safe value,

or the resistor 15 may be so designed that the safe maximum temperature cannot be exceeded. This temperature of 1600 degrees C. however is not hlgh enough to form the brazed connection 27. Consequently, after the point 27 has reached the temperature of the furnace, it is still further heated in the furnace but independently of the furnace temperature b energizing the high frequency coil 10 where y additional heat is induced in the parts 26 and 27 to raise the temperature ofthe parts to the brazing temperature, ap-

proximately 1755 degrees C.

It will be understood that the resistor 15 may or may not be used while the high freuency heating oil is being used, as desired. ith the furnace wall heat insulated as shown, however, heat is dissipated from the heatlng chamber at a very low rate, and consequently satisfactory operation may be obtained by deenergizing the resistor while the high frequency source of heat is being used. In any case, however, the high frequency source of heat is used to supplement the resistor, and whether the resistor is actually generating heatzor not when'the hi h frequency source of heat is being used, t e

furnace itself is still heated to its maximum temperature and thus functions as a source of heat tending that, temperature. a

While I have described my invention as embodied in concrete form and as operating in.- a-'specific manner in accordance with the to maintain the charge at provisions of the patent statutes, it should be understood that-I do not limit my, invention thereto, since various modifications thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by. Letters Patent of the United States is:

1. The method of heating which consists in heating the charge in a furnace to the temperature of the furnace, and then maintaining the charge in the furnace while still further heating the charge by heat generated in the charge itself independently of the furnace temperature.

2. The method of heating wherein a furnace is used which consists in maintaining the furnace at a predetermined temperature,

placing the charge in the furnace and allowing it to be heated to approximately said temperature, and then subjecting the charge while still in said furnace to an alternating magneticfield of relatively high frequency so as to heat the charge to a still higher temperature.

3. The method of heating which consists in heating the charge in a furnace to the maximum temperature of the furnace, and then subjecting the charge to a high frequency field while still in said furnace so as to heat the charge to a still higher temperature.

4. The combination with an electric furnace provided with electric heating means for heating said furnace to a predetermined temperature, of a high frequency winding surrounding said furnace and means for supplying a high frequency current to said winding.

5. The combination with a furnace structure comprising walls forming a heating chamber, of means for heating said chamber to a predetermined temperature, and auxiliary means for heating the charge in said chamber independently of the temperature of said chamber comprising a winding in inductive relation with a charge in said cham- 

